docs: def mesh_nmasked(self):
          """
          A 2D (masked) array of the number of masked pixels in each mesh.
          Only meshes included in the background estimation are included.
          The array is masked only if meshes were excluded.
          """
  
          return self._make_2d_array(
              np.ma.count_masked(self._data_sigclip, axis=1))